1. Technical Field
The present inventions relate to radar systems which measure characteristics of detected objects and, more particularly, relate to calibrated radar systems useful for at least applications which measure characteristics of detected objects in the near field of the radar system.
2. Description of the Related Art
Radar systems have been used for distance ranging and speed determination. Frequency Modulated Continuous Wave (FMCW) is one common form of radar signaling. Accuracy of determinations of speed or distance ranging has been improved using calibration.
One traditional way for detection of targets with a radar system is to transmit a carrier signal of a known strength and frequency, which then reflects off the target of interest, and then the signal is received by the radar unit. This received signal is then mixed with the transmitted signal, and any frequency difference between the two signals (the “mixing product”) results in what is known as a “beat note”, which is a low-frequency signal (often less than 1000 Hz) which represents the instantaneous difference of the frequencies being transmitted and received. The farther away the target, the greater the frequency difference, which results in a higher frequency beat note. This signaling method used for these systems is called: frequency modulated continuous wave (FMCW).
For typical open-air applications (such as vehicle collision avoidance, presence detection for security or lighting control, and automatic door opening), the FCC limits the range of frequencies allowed. For example, in the 24 GHz band, the limits are 100 MHz or 250 MHz depending on the application. This band limit, in turn, limits how high in frequency a beat note can be effectively generated for a target at a given range.
In traditional FMCW radar systems, the detection and measurement of targets is done by analyzing the beat note with a Fast Fourier Transform (FFT), which provides a means of directly measuring frequency of the beat note. This worked well when there was an entire cycle of the beat note inside the time window of interest.
For typical applications of radar (vehicle collision avoidance; tank level monitoring for large, open, non-metallic tanks; presence detection for security or lighting control; automatic door opening) operating in the above restricted frequency bands, the beat note is still sufficiently high enough in frequency for targets beyond about the 2 meter range. Therefore with the traditional FFT technique, it is possible to reliably detect targets beyond about the 2 meter range.
Other use cases require detection and distance measurements of targets within the near field (less than about 2 meters) of the radar sensing system. These use cases include tank level monitoring for small, open air tanks; collision avoidance for objects within inches of each other; location of in-wall objects (pipes, conduit, studs), gesture detection; and others.
Near field determinations of distance ranging and speed determination have been attempted and suffer from inaccuracies the shorter the near field. What is needed is improved accuracy in radar systems especially in near field applications.